The present invention relates to a control arrangement for controlling the operation of a grabbing crane for handling bulk material, particularly a bridge grabbing crane for loading and unloading bulk material into and from a ship.
DE-AS No. 10 82 837 discloses an arrangement for controlling the operation of a grabbing crane in which the position of the grab bucket is remotely displayed by means of a television camera and a television screen. The actual position of the crane carriage within a range defined by markings on a stationary part of the crane in the field of view of the camera is displayed on the screen together with markings corresponding to those on the crane. It is the crane operator's responsibility to move the grab bucket so that its actual position is always within the marked range.
DE-PS No. 26 42 181 describes a device for displaying the position of the grab bucket on a display which is divided into a multiplicity of fields each containing two light-emitting diodes. One of the two light-emitting diodes is always driven by a set or desired-value transmitter and the other light-emitting diode by an actual-value transmitter, so that the desired and actual positions of the grab bucket are each represented by a light spot travelling across the display as the grab bucket moves. To initiate a loading or unloading process, the crane operator places the grab bucket on the bulk material through manual control and aligns a scaled template which corresponds to the cross section of a ship's hold on the display screen in accordance with the displayed actual position of the grab bucket. This enables the crane operator to set the desired values required for operation of the grab bucket within the template. The respectively set initial desired values are retained for several grabbing cycles as controlled by a marking-line computer. However, the operating range of the grab bucket cannot be determined with sufficient accuracy by approaching a target position only once and aligning the template on the display screen in dependence thereon to insure that collisions of the grab bucket with edges of the ship's hatches do not occur.